Alcohol-Induced Mitochondrial Dysfunction and the Hepatocyte Clock

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 DESCRIPTION (provided by applicant): Alcoholic liver disease (ALD) is a major cause of morbidity and mortality from chronic alcohol consumption. Despite increased medical and scientific knowledge of ALD, the molecular events responsible for ALD remain poorly understood. Previous studies from our labs have shown that mitochondrial bioenergetic function is severely compromised in the liver following chronic alcohol consumption and is a significant causative factor for hepatocyte necrosis. However, the mechanisms responsible for mitochondrial damage remain unknown. We propose that disruption in the hepatocyte molecular circadian clock underpins chronic alcohol-induced mitochondrial dysfunction. Published studies have shown that the clock influences hepatic oxidative metabolism (β-oxidation) and that key regulators of mitochondrial biogenesis (Pgc1a) exhibit diurnal rhythms in peripheral tissues. Importantly, we have found that rhythms in Pgc1a, Pgc1b, and Pdk4 are significantly dampened in livers of alcohol-fed mice, suggesting that the ability of mitochondria to be metabolically flexible and responsive to time-of-day dependent fluctuations in energetic supply and demand is severely compromised in the chronic alcohol-exposed liver. In line with this, we observed that the transcription factor, nuclear respiratory factor 1 (Nrf1), which is essential for integration o nuclear and mitochondrial encoded gene transcription exhibits a diurnal rhythm, that is abolished by genetic disruption of the circadian clock in the liver. Moreover, we found that the activity of cytochrome c oxidase, the terminal and rate-limiting enzyme of the mitochondrial respiratory chain, displays a robust diurnal rhythm in liver mitochondria from control mice that is significantly depressed by chronic alcohol. Taken together, these new data strongly suggest that the circadian clock regulates mitochondrial function over the course of the day, and that disruption in these rhythms by chronic alcohol impairs hepatic bioenergetic function. Accordingly, our long-term goal is to test the hypothesis that chronic alcohol-mediated disruption in the liver clock is a critical mechanism underpinning hepatic mitochondrial dysfunction in the chronic alcohol consumer. To test this hypothesis we propose the following Aims. In Aim 1, we will determine whether the hepatocyte clock directly regulates mitochondrial bioenergetics and influences chronic alcohol-induced mitochondrial dysfunction in the liver. In Aim 2, we will determine whether alcohol-mediated alterations in the hepatocyte clock and impairments in liver mitochondrial bioenergetics can be treated with a drug (an ROR ligand) targeting the clock. This project will be facilitated by using a genetic mouse model in which the hepatocyte circadian clock is nonfunctional, namely the hepatocyte- specific BMAL1 knockout mouse. In summary, these innovative studies will provide new insight regarding the mechanisms by which the circadian clock regulates cellular bioenergetic homeostasis and reveal that chronic alcohol-mediated disruption to the clock contributes to mitochondrial dysfunction in the liver. Moreover, this work will likely lay a foundation for future pharmacological studies targeting the clock in treating ALD patients.